U.S. patent application number 14/526387 was filed with the patent office on 2015-06-11 for negative active material, lithium battery including the material, and method of manufacturing the material.
The applicant listed for this patent is Samsung SDI Co., Ltd.. Invention is credited to Dong-Hee Han, Jae-Myung Kim, Hyun-Ki Park, Sang-Eun Park.
Application Number | 20150162604 14/526387 |
Document ID | / |
Family ID | 52101081 |
Filed Date | 2015-06-11 |
United States Patent
Application |
20150162604 |
Kind Code |
A1 |
Park; Sang-Eun ; et
al. |
June 11, 2015 |
NEGATIVE ACTIVE MATERIAL, LITHIUM BATTERY INCLUDING THE MATERIAL,
AND METHOD OF MANUFACTURING THE MATERIAL
Abstract
A negative active material, a negative electrode, a lithium
battery including the negative active material, and a method of
preparing the negative active material. The negative active
material includes a crystalline carbonaceous substrate; and metal
oxide nanoparticles disposed on a surface of the crystalline
carbonaceous substrate, wherein the metal oxide nanoparticles have
a rutile structure. The negative active material may be used to
improve high temperature stability and lifespan characteristics of
a lithium battery.
Inventors: |
Park; Sang-Eun; (Yongin-si,
KR) ; Kim; Jae-Myung; (Yongin-si, KR) ; Park;
Hyun-Ki; (Yongin-si, KR) ; Han; Dong-Hee;
(Yongin-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung SDI Co., Ltd. |
Yongin-si |
|
KR |
|
|
Family ID: |
52101081 |
Appl. No.: |
14/526387 |
Filed: |
October 28, 2014 |
Current U.S.
Class: |
429/231.8 ;
252/182.1 |
Current CPC
Class: |
H01M 4/1393 20130101;
H01M 4/133 20130101; H01M 4/587 20130101; H01M 4/62 20130101; H01M
10/0525 20130101; H01M 4/0471 20130101; Y02E 60/10 20130101; H01M
4/366 20130101 |
International
Class: |
H01M 4/36 20060101
H01M004/36; H01M 10/052 20060101 H01M010/052; H01M 4/04 20060101
H01M004/04; H01M 4/587 20060101 H01M004/587; H01M 4/62 20060101
H01M004/62 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2013 |
KR |
10-2013-0153308 |
Claims
1. A negative active material comprising: a crystalline
carbonaceous substrate; and metal oxide nanoparticles on a surface
of the crystalline carbonaceous substrate.
2. The negative active material of claim 1, wherein the metal oxide
nanoparticles have a rutile structure.
3. The negative active material of claim 1, wherein the metal oxide
nanoparticles have a rutile structure mixed with an anatase
structure.
4. The negative active material of claim 1, wherein the metal oxide
nanoparticles comprise at least one metal oxide of a metal selected
from the elements of Group 2 to Group 13.
5. The negative active material of claim 1, wherein the metal oxide
nanoparticles comprise an oxide of at least one metal selected from
the group consisting of zirconium (Zr), nickel (Ni), cobalt (Co),
manganese (Mn), boron (B), magnesium (Mg), calcium (Ca), strontium
(Sr), barium (Ba), titanium (Ti), vanadium (V), iron (Fe), copper
(Cu), chromium (Cr), zinc (Zn), molybdenum (Mo), niobium (Nb),
tantalum (Ta), and aluminum (Al).
6. The negative active material of claim 1, wherein the metal oxide
nanoparticles comprise at least one selected from the group
consisting of titanium oxide, aluminum oxide, chromium trioxide,
zinc oxide, copper oxide, magnesium oxide, zirconium dioxide,
molybdenum trioxide, vanadium pentoxide, niobium pentoxide, and
tantalum pentoxide.
7. The negative active material of claim 1, wherein the metal oxide
nanoparticles comprise titanium oxide having a rutile
structure.
8. The negative active material of claim 1, wherein the metal oxide
nanoparticles comprise a titanium oxide having a rutile structure
mixed with an anatase structure.
9. The negative active material of claim 1, wherein an average
diameter of the metal oxide nanoparticles is about 1 nm to about 30
nm.
10. The negative active material of claim 1, wherein the metal
oxide nanoparticles comprise a coating layer having an island shape
on a surface of the crystalline carbonaceous substrate.
11. The negative active material of claim 1, wherein the
crystalline carbonaceous substrate comprises at least one of
natural graphite, artificial graphite, expandable graphite,
graphene, carbon black, and fullerene soot.
12. The negative active material of claim 1, wherein the
crystalline carbonaceous substrate has a spherical form, a planar
form, a fiber form, a tube form, and/or a powder form.
13. The negative active material of claim 1, wherein an average
diameter of the crystalline carbonaceous substrate is about 1 .mu.m
to about 30 .mu.m.
14. The negative active material of claim 1, wherein an amount of
the metal oxide nanoparticles is about 0.01 parts by weight to
about 10 parts by weight based on 100 parts by weight of the
crystalline carbonaceous substrate.
15. A lithium battery comprising the negative active material
according to claim 1 in a negative electrode.
16. A method of preparing a negative active material, the method
comprising: mixing a crystalline carbonaceous substrate, a metal
oxide precursor, and a solvent to prepare a mixture solution;
drying the mixture solution to prepare a dried product; and heat
treating the dried product.
17. The method of claim 16, wherein the metal oxide precursor is a
metal salt comprising at least one metal selected from the group
consisting of titanium (Ti), zirconium (Zr), nickel (Ni), cobalt
(Co), manganese (Mn), chromium (Cr), zinc (Zn), boron (B),
magnesium (Mg), calcium (Ca), strontinum (Sr), barium (Ba),
vanadium (V,) iron (Fe), copper (Cu), molybdenum (Mo), niobium
(Nb), tantalum (Ta), and aluminum (Al).
18. The method of claim 16, wherein a weight ratio of the
crystalline carbonaceous substrate to the metal oxide precursor is
about 100:0.01 to about 100:20.
19. The method of claim 16, wherein the heat treating is performed
in a nitrogen atmosphere or an air atmosphere at a temperature of
700.degree. C. or greater.
20. The method of claim 19, wherein the heat treating is performed
in the nitrogen atmosphere or the air atmosphere at a temperature
of about 700.degree. C. to about 900.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2013-0153308, filed on Dec. 10,
2013, in the Korean Intellectual Property Office, the disclosure of
which is incorporated herein in its entirety by reference.
BACKGROUND
[0002] 1. Field
[0003] One or more embodiments of the present invention relate to a
negative active material, a lithium battery including the negative
active material, and a method of manufacturing the negative active
material.
[0004] 2. Description of the Related Art
[0005] Lithium secondary batteries used in portable electronic
devices for information communication (such as personal digital
assistants (PDAs), mobile phones, or notebook computers), electric
bicycles, electric vehicles, or the like, have a discharge voltage
that is at least twice as high as that of a comparable
(conventional) battery, and thus, have a high energy density.
[0006] Lithium secondary batteries generate electric energy by
oxidation and reduction reactions occurred when lithium ions are
intercalated/deintercalated into/from a positive electrode and a
negative electrode (each including an active material that enables
intercalation and deintercalation of lithium ions), with an organic
electrolytic solution or a polymer electrolytic solution interposed
between the positive and negative electrodes.
[0007] Research is being conducted about various forms of
carbonaceous materials (such as synthetic and natural graphite, or
hard carbon), which are capable of intercalation/deintercalation of
lithium, and non-carbonaceous materials such as Si.
[0008] When a negative electrode material of a lithium secondary
battery directly contacts an electrolyte, the electrolyte may
undergo reductive cleavage at a low electric potential.
Accordingly, during a charging process of lithium, reactivity
between the negative electrode material and the electrolyte of the
lithium secondary battery may increase to form a thin film on a
surface of the negative electrode. Here, the higher the temperature
of the reaction in the battery, the greater the reactivity between
the negative electrode material and the electrolyte. Due to the
thin film, lithium ions and electrons are consumed, thereby
deteriorating lifespan characteristics of the lithium secondary
battery. Also, the film undergoes exothermal decomposition reaction
at a high temperature of about 100.degree. C. or greater, and as
the amount of the film increases, the amount of heating increases,
which may deteriorate the high temperature stability of a cell. Due
to this phenomenon, high temperature stability and lifespan
characteristics of a lithium secondary battery may deteriorate.
[0009] Accordingly, development of a negative active material
having improved high temperature stability and lifespan
characteristics is needed.
SUMMARY
[0010] An aspect according to one or more embodiments of the
present invention is directed toward negative active materials that
may improve high temperature stability and lifespan characteristics
of lithium batteries.
[0011] An aspect according to one or more embodiments of the
present invention is directed toward negative electrodes including
the negative active materials.
[0012] An aspect according to one or more embodiments of the
present invention is directed toward lithium batteries including
the negative electrodes.
[0013] An aspect according to one or more embodiments of the
present invention is directed toward methods of preparing the
negative active materials.
[0014] Additional aspects will be set forth in part in the
description which follows and, in part, will be apparent from the
description, or may be learned by practice of the presented
embodiments.
[0015] According to one or more embodiments of the present
invention, a negative active material includes:
[0016] a crystalline carbonaceous substrate; and
[0017] metal oxide nanoparticles on a surface of the crystalline
carbonaceous substrate.
[0018] According to one or more embodiments of the present
invention, the metal oxide nanoparticles may have a rutile
structure.
[0019] According to one or more embodiments of the present
invention, the metal oxide nanoparticles may have a rutile
structure mixed with an anatase structure.
[0020] According to one or more embodiments of the present
invention, the metal oxide nanoparticles may include at least one
metal oxide of a metal selected from the elements of Group 2 to
Group 13.
[0021] According to one or more embodiments of the present
invention, the metal oxide nanoparticles may include an oxide of at
least one metal selected from the group consisting of zirconium
(Zr), nickel (Ni), cobalt (Co), manganese (Mn), boron (B),
magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium
(Ti), vanadium (V), iron (Fe), copper (Cu), chromium (Cr), zinc
(Zn), molybdenum (Mo), niobium (Nb), tantalum (Ta), and aluminum
(Al).
[0022] According to one or more embodiments of the present
invention, the metal oxide nanoparticles may include a metal oxide
represented by Formula 1 below.
M.sub.aO.sub.b Formula 1
[0023] in Formula 1,
[0024] 1.ltoreq.a.ltoreq.4, 1.ltoreq.b.ltoreq.10, and
[0025] M may be at least one selected from the group consisting of
titanium (Ti), zirconium (Zr), nickel (Ni), cobalt (Co), manganese
(Mn), chromium (Cr), zinc (Zn), boron (B), magnesium (Mg), calcium
(Ca), strontium (Sr), barium (Ba), vanadium (V), iron (Fe), copper
(Cu), molybdenum (Mo), niobium (Nb), tantalum (Ta), and aluminum
(Al).
[0026] According to one or more embodiments of the present
invention, the metal oxide nanoparticles may include at least one
selected from the group consisting of titanium oxide, aluminum
oxide, chromium trioxide, zinc oxide, copper oxide, magnesium
oxide, zirconium dioxide, molybdenum trioxide, vanadium pentoxide,
niobium pentoxide, and tantalum pentoxide.
[0027] According to one or more embodiments of the present
invention, the metal oxide nanoparticles may include titanium oxide
having a rutile structure.
[0028] According to one or more embodiments of the present
invention, the metal oxide nanoparticles may include a titanium
oxide having a rutile structure mixed with an anatase
structure.
[0029] According to one or more embodiments of the present
invention, an average diameter of the metal oxide nanoparticles may
be about 1 nm to about 30 nm.
[0030] According to one or more embodiments of the present
invention, the metal oxide nanoparticles may include a coating
layer having an island shape (as a discontinuous layer) on a
surface of the crystalline carbonaceous substrate.
[0031] According to one or more embodiments of the present
invention, the crystalline carbonaceous substrate may include at
least one of natural graphite, artificial graphite, expandable
graphite, graphene, carbon black, and fullerene soot.
[0032] According to one or more embodiments of the present
invention, the crystalline carbonaceous substrate may have a
spherical form, a planar form, a fiber form, a tube form, or a
powder form.
[0033] According to one or more embodiments of the present
invention, an average diameter of the crystalline carbonaceous
substrate may be about 1 .mu.m to about 30 .mu.m.
[0034] According to one or more embodiments of the present
invention, an amount of the metal oxide nanoparticles may be about
0.01 parts by weight to about 10 parts by weight based on 100 parts
by weight of the crystalline carbonaceous substrate.
[0035] According to one or more embodiments of the present
invention, a negative electrode includes the said negative active
material.
[0036] According to one or more embodiments of the present
invention, a lithium battery includes the said negative
electrode.
[0037] According to one or more embodiments of the present
invention, a method of preparing a negative active material
includes:
[0038] mixing a crystalline carbonaceous substrate, a metal oxide
precursor, and a solvent to prepare a mixture solution;
[0039] drying the mixture solution to prepare a dried product;
and
[0040] heat treating the dried product.
[0041] According to one or more embodiments of the present
invention, the metal oxide precursor may be a metal salt including
at least one metal selected from the group consisting of titanium
(Ti), zirconium (Zr), nickel (Ni), cobalt (Co), manganese (Mn),
chromium (Cr), zinc (Zn), boron (B), magnesium (Mg), calcium (Ca),
strontinum (Sr), barium (Ba), vanadium (V,) iron (Fe), copper (Cu),
molybdenum (Mo), niobium (Nb), tantalum (Ta), and aluminum
(Al).
[0042] According to one or more embodiments of the present
invention, a weight ratio of the crystalline carbonaceous substrate
to the metal oxide precursor may be about 100:0.01 to about
100:20.
[0043] According to one or more embodiments of the present
invention, the heat treating may be performed in a nitrogen
atmosphere or an air atmosphere at a temperature of 700.degree. C.
or greater.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] These and/or other aspects will become apparent and more
readily appreciated from the following description of the
embodiments, taken in conjunction with the accompanying drawings in
which:
[0045] FIG. 1 is a schematic view showing a structure of a negative
active material according to an embodiment;
[0046] FIG. 2A shows a structure of a rutile unit cell and FIG. 2B
shows a structure of an anatase unit cell;
[0047] FIG. 3 is a schematic view showing a structure of a lithium
battery according to an embodiment;
[0048] FIGS. 4A and 4B are Field Emission Scanning Electron
Microscope (FE-SEM) images of graphite substrates before and after
heat treatment in Manufacturing Example 1;
[0049] FIG. 5 shows x-ray diffraction (XRD) analysis results of the
negative active material used in Manufacturing Examples 1 and 2 and
Comparative Manufacturing Example 1;
[0050] FIG. 6 shows XRD analysis results showing a crystalline
phase of TiO.sub.2 according to a heat treatment temperature;
[0051] FIG. 7 shows impedance measurement results after high
temperature storage of coin half-cells manufactured in Example 2
and Comparative Example 1;
[0052] FIG. 8 shows thermal stability measurement results of coin
half-cells manufactured in Example 1 and Comparative Example 1;
[0053] FIG. 9 is a graph showing high temperature lifespan
characteristics of coin full cells manufactured in Examples 3 and 4
and Comparative Examples 2 and 3.
DETAILED DESCRIPTION
[0054] Reference will now be made in detail to embodiments,
examples of which are illustrated in the accompanying drawings,
wherein like reference numerals refer to like elements throughout.
Here, the present embodiments may have different forms and should
not be construed as being limited to the descriptions set forth
herein. Accordingly, the embodiments are merely described below, by
referring to the figures, to explain aspects of the present
description. As used herein, the term "and/or" includes any and all
combinations of one or more of the associated listed items.
Expressions such as "at least one of," when preceding a list of
elements, modify the entire list of elements and do not modify the
individual elements of the list. Further, the use of "may" when
describing embodiments of the present invention refers to "one or
more embodiments of the present invention."
[0055] Hereinafter, embodiments of the present invention will be
described in greater detail.
[0056] A negative active material according to an embodiment of the
present invention includes:
[0057] a crystalline carbonaceous substrate; and
[0058] metal oxide nanoparticles disposed on a surface of the
crystalline carbonaceous substrate.
[0059] FIG. 1 is a schematic view showing a structure of a negative
active material 10 according to an embodiment. As shown in FIG. 1,
the negative active material 10 has metal oxide nanoparticles 12
disposed on a surface of a crystalline carbonaceous substrate
11.
[0060] The crystalline carbonaceous substrate 11 includes
crystalline carbon. Here, the term "carbonaceous substrate" refers
to a substrate including about 50 wt % of carbon. For example, the
carbonaceous substrate may include at least about 60 wt %, about 70
wt %, about 80 wt %, about 90 wt %, or about 100 wt % of carbon.
Also, the term "crystalline" as used herein refers to inclusion of
about 50 wt % of a hexagonal crystal lattice in which 3 different
carbon atoms are covalently bonded to a carbon atom having an
sp.sup.2 hybrid orbital. For example, the crystalline carbonaceous
substrate 11 may include about 60 wt %, about 70 wt %, about 80 wt
%, about 90 wt %, or about 100 wt % of crystalline carbon. A
hexahedral crystal lattice structure may have a single layer
structure or a multi-layer structure, or may have various deformed
structures of a 2-dimensional form due to bending, winding,
rolling, partial damage, or the like, and the hexahedral crystal
lattice structure may be connected in the form of a soccer ball. A
crystal structure of the crystalline carbonaceous substrate 11 is
not particularly limited as long as the structure enables a
reversible intercalation and deintercalation of lithium ions during
charge and discharge processes.
[0061] According to an embodiment, the crystalline carbonaceous
substrate 11 may be natural graphite, artificial graphite,
expandable graphite, graphene, carbon black, fullerene soot, or a
combination thereof, but the crystalline carbonaceous substrate 11
is not limited thereto.
[0062] Natural graphite is a naturally available graphite such as
flake graphite, high crystalline graphite, or microcrystalline (or
cryptocrystalline) graphite. Artificial graphite is artificially
synthesized graphite, which may be prepared by heat-treating
amorphous carbon at a high temperature, and examples of the
artificial graphite include primary graphite, electrographite,
secondary graphite, and graphite fiber. Expandable graphite refers
to graphite prepared by intercalating a chemical such as an acid or
a base between layers of the graphite structure, heat-treating the
same, and then expanding a vertical layer of a molecular structure.
Graphene refers to a single layer graphite. Carbon black is a
crystalline material having a smaller-sized regularity than
graphite, and when carbon black is heated at a temperature of about
3,000.degree. C. for a long time, carbon black may transform into
graphite. Fullerene soot is a carbon compound in which fullerene
having a polyhedral bundle formed of 60 or more carbon atoms is
included in an amount of about 3 wt %. The crystalline carbonaceous
substrate 11 may be formed of one kind of crystalline carbonaceous
material or a combination of two or more crystalline carbonaceous
materials. For example, natural graphite and/or artificial graphite
may be used because a mixture density may be easily increased
during the preparation of a negative electrode.
[0063] The crystalline carbonaceous substrate 11 may be included in
a spherical form, a planar form, a fiber form, a tube form, and/or
a powder form. For example, the crystalline carbonaceous substrate
11 may have a spherical form and/or a planar form. Though FIG. 1
shows one embodiment where the crystalline carbonaceous substrate
11 has a spherical form, the crystalline carbonaceous substrate 11
is not limited thereto.
[0064] The crystalline carbonaceous substrate 11 having a spherical
form may be manufactured by, for example, spheronization of
crystalline carbon. For example, the carbonaceous substrate having
a spherical structure formed by the spheronization of graphite may
have graphite of a layered structure curved or bent, or may have a
microstructure formed of a plurality of curved or bent graphite
sheets having a scale-like form or scale form.
[0065] When the crystalline carbonaceous substrate 11 has a
spherical form, a sphericity of the crystalline carbonaceous
substrate 11 may about 0.7 to about 1.0. The sphericity refers a
value measuring the extent of deformation of a sphere from an ideal
sphere, and the value thereof may be in a range of 0 to 1.0,
wherein when the value is closer to 1.0, the sphere is closer to
the ideal sphere. For example, the sphericity of the crystalline
carbonaceous substrate 11 may be 0.8 to 1.0. For example, the
sphericity of the crystalline carbonaceous substrate 11 may be 0.9
to 1.0. On the other hand, the sphericity of a carbonaceous
substrate having a planar form may be 0.7 or less.
[0066] The crystalline carbonaceous substrate 11 may include pores
therein when the crystalline carbonaceous substrate 11 is formed
into a spherical form through a spheronization process. A porosity
of the crystalline carbonaceous substrate 11 may be about 5% to
about 30% based on a total volume of the crystalline carbonaceous
substrate 11, for example, may be about 10% to about 20%.
[0067] An average diameter of the crystalline carbonaceous
substrate 11 is not particularly limited, but when the average
diameter is too small, the crystalline carbonaceous substrate 11
may be highly reactive to electrolyte, which may deteriorate cycle
characteristics, and when the average diameter is too big,
dispersion stability of the crystalline carbonaceous substrate 11
during the preparation of a negative electrode slurry may
deteriorate such that a surface of the negative electrode may be
rough. For example, the average diameter of the crystalline
carbonaceous substrate 11 may be about 1 .mu.m to about 30 .mu.m.
In one embodiment, for example, the average diameter of the
crystalline carbonaceous substrate 11 may be about 5 .mu.m to about
25 .mu.m, or, may be about 10 .mu.m to about 20 .mu.m.
[0068] The metal oxide nanoparticles 12 may be disposed on the
surface of the crystalline carbonaceous substrate 11.
[0069] A metal of the metal oxide in the metal oxide nanoparticles
12 may be at least one selected from the elements of Group 2 to
Group 13 in the periodic table of elements. Accordingly, elements
of Group 1 and Groups 14 to 16 in the periodic table of elements
are not included in the metal of the metal oxide.
[0070] For example, the metal of the metal oxide may be at least
one metal selected from the group consisting of titanium (Ti),
zirconium (Zr), nickel (Ni), cobalt (Co), manganese (Mn), chromium
(Cr), zinc (Zn), boron (B), magnesium (Mg), calcium (Ca), strontium
(Sr), barium (Ba), vanadium (V), iron (Fe), copper (Cu), molybdenum
(Mo), niobium (Nb), tantalum (Ta), and aluminum (Al).
[0071] For example, the metal oxide may be represented by Formula 1
below:
M.sub.aO.sub.b Formula 1
[0072] In Formula 1, 1.ltoreq.a.ltoreq.4, 1.ltoreq.b.ltoreq.10, and
M is at least one selected from the group consisting of Ti, Zr, Ni,
Co, Mn, Cr, Zn, B, Mg, Ca, Sr, Ba, V, Fe, Cu, Mo, Nb, Ta, and
Al.
[0073] For example, the metal oxide may include at least one
selected from the group consisting of titanium oxide, aluminum
oxide, chromium trioxide, zinc oxide, copper oxide, magnesium
oxide, zirconium dioxide, molybdenum trioxide, vanadium pentoxide,
niobium pentoxide, and tantalum pentoxide. For example, as the
metal oxide, TiO.sub.x (1.ltoreq.x.ltoreq.2), Al.sub.2O.sub.3,
ZrO.sub.2, or the like may be used. For example, as the metal
oxide, TiO.sub.x (1.ltoreq.x.ltoreq.2), for example, TiO.sub.2 may
be used.
[0074] The average diameter of the metal oxide nanoparticles 12 may
be about 1 nm to about 30 nm, about 5 nm to about 25 nm, or about
10 nm to about 20 nm.
[0075] The metal oxide nanoparticles 12 may form a coating layer on
the surface of the crystalline carbonaceous substrate 11. As such,
the coating layer formed of the metal oxide nanoparticles 12 may
exist between the crystalline carbonaceous substrate 11 and the
electrolyte to increase the interface stability of the crystalline
carbonaceous substrate 11, and thereby improve lifespan
characteristics and the high temperature stability.
[0076] TiO.sub.x (1.ltoreq.x.ltoreq.2), for example, TiO.sub.2, has
a high capacity retention rate, a low self-discharge rate, and low
volumetric expansion characteristics, and has low high temperature
heat generation characteristics at a charge voltage of graphite
(0.1 V). TiO.sub.x has a small but sufficient lithium ion
conductivity between about 1.5 V to about 0 V, and thus, TiO.sub.x
may not only act as a barrier for blocking direct contact between
the electrolyte and the crystalline carbonaceous substrate 11, but
also as a pathway for lithium ions.
[0077] The metal oxide nanoparticles 12 may be inactive to lithium.
For example, the metal oxide does not react with lithium such that
lithium metal oxide may not be formed. In other words, the metal
oxide is not a negative active material capable of
intercalation/deintercalation of lithium, but a conductor, which
provides a simple transfer pathway of lithium ions and/or
electrons, and also acts as a protective layer for reducing or
preventing a side reaction with the electrolyte. Alternatively, the
metal oxide nanoparticles 12 may be an electrical insulator and may
form a protective layer that reduces or prevents a side reaction
with the electrolyte.
[0078] According to an embodiment, the metal oxide nanoparticles 12
may have a rutile structure. The rutile structure may be formed by
a titanium oxide having a microcrystalline lattice form, but the
rutile structure is not limited thereto.
[0079] FIG. 2A shows a structure of a rutile unit cell, and FIG. 2B
shows a structure of an anatase unit cell. The conclusion that
metal oxide nanoparticles having a rutile structure may have a
better high temperature stability than metal oxide nanoparticles
having an anatase structure may be based on the following
embodiments.
[0080] According to an embodiment, metal oxide nanoparticles may
have a combination (mixed) structure of a rutile structure and an
anatase structure. For example, metal oxide nanoparticles may
include titanium oxide having a structure of a rutile structure and
an anatase structure.
[0081] A method of forming the rutile structure may be any suitable
method known in the art, and is not particularly limited. To
prepare the metal oxide nanoparticles having a rutile structure,
for example, a crystalline carbonaceous substrate may be coated
with a coating solution including a metal oxide precursor and then
heat treated at a temperature of about 700.degree. C. or greater.
The rutile structure may be identified by x-ray diffraction
spectroscopy.
[0082] In a negative active material, an amount of the metal oxide
nanoparticles may be about 0.01 parts by weight to about 10 parts
by weight based on 100 parts by weight of the crystalline
carbonaceous substrate. For example, the amount of the metal oxide
nanoparticles may be about 0.1 wt % to about 5 wt % or about 0.5 wt
% to about 2 wt %, based on the total weight of the negative active
material. In one embodiment, when the amount of the coating layer
is in the range described above, lifespan characteristics of a
lithium battery is effectively improved.
[0083] As described above, the negative active material, in which
the metal oxide nanoparticles are disposed on the surface of the
crystalline carbonaceous substrate, may increase the interface
stability between the crystalline carbonaceous substrate and the
electrolyte to have (improve) a long lifespan, a high temperature
lifespan, and a high temperature stability.
[0084] A negative electrode according to another embodiment
includes the negative active material described above.
[0085] The negative electrode may be prepared by, for example,
molding a negative active material composition including a negative
active material, a binder, and optionally, a conductive agent in a
set or predetermined shape, or coating the negative active material
composition on a current collector such as a copper foil.
[0086] In one embodiment, a negative active material composition
including a mixture of a negative active material, a conductive
agent, a binder, and a solvent is prepared. The negative active
material composition is directly coated on a metal current
collector to manufacture a negative electrode plate. Alternatively,
the negative active material composition may be cast on a separate
support, and then a film may be peeled off from the support and
then laminated on a metal current collector to manufacture a
negative electrode plate. The form of the negative electrode is not
limited to the forms listed above and may differ from the forms
described above.
[0087] The negative active material composition may further include
a negative electrode material conventionally used as the negative
active material in a lithium battery of the related art, in
addition to the negative active material described above. For
example, the negative active material composition may further
include at least one selected from the group consisting of lithium
metal, a metal alloyable with lithium, a transition metal oxide, a
non-transitional metal oxide, and a carbonaceous material.
[0088] For example, the metal alloyable with lithium may be silicon
(Si), tin (Sn), aluminum (Al), germanium (Ge), lead (Pb), bismuth
(Bi), antimony (Sb), a Si--Y alloy (wherein, Y is an alkali metal,
an alkaline earth metal, a Group 13 element other than Si, a Group
14 element, a transition metal, a rare earth metal element, or a
combination thereof), and a Sn--Y alloy (wherein Y is an alkali
metal, an alkaline earth metal, a Group 13 element, a Group 14
element other than Sn, a transition metal, a rear earth metal
element, or a combination thereof). The element Y may be magnesium
(Mg), calcium (Ca), strontium (Sr), barium (Ba), radon (Ra),
scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium
(Hf), rutherfordium (Rf), vanadium (V), niobium (Nb), tantalum
(Ta), dubium (Db), chromium (Cr), molybdenum (Mo), tungsten (W),
seaborgium (Sg), technetium (Tc), rhenium (Re), bohrium (Bh), iron
(Fe), lead (Pb), ruthenium (Ru), osmium (Os), hassium (Hs), rhodium
(Rh), iridium (Ir), palladium (Pd), platinum (Pt), copper (Cu),
silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), boron (B),
aluminum (Al), gallium (Ga), tin (Sn), indium (In), germanium (Ge),
phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur
(S), selenium (Se), tellurium (Te), polonium (Po), or a combination
thereof.
[0089] For example, the transition metal oxide may be lithium
titanium oxide, vanadium oxide, or lithium vanadium oxide.
[0090] For example, the transition metal oxide may be SnO.sub.2 or
SiO.sub.x (0<x<2).
[0091] Examples of the carbonaceous material include crystalline
carbon, amorphous carbon, or a mixture thereof. The crystalline
carbon may be graphite such as natural graphite or synthetic
graphite having an irregular form, a planar form, a flake form, a
spherical form, or a fiber form, and the amorphous carbon may be
soft carbon (low temperature calcined carbon), hard carbon,
mesophase pitch carbide, calcined coke, or a combination
thereof.
[0092] The binder may be any suitable binder used in the art such
as polyvinylidene fluoride, polyvinylidene chloride,
polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile,
polyvinyl alcohol, carboxymethyl cellulose (CMC), starch,
hydroxypropyl cellulose, regenerated cellulose,
polyvinylpyrrolidone, polyethylene, polypropylene, polystyrene,
polymethyl methacrylate, polyaniline, acrylonitrile butadiene
styrene, phenol resin, epoxy resin, polyethylene terephthalate,
polytetrafluoroethylene, polyphenylene sulfide, polyamideimide,
polyetherimide, polyethylenesulfone, polyamide, polyacetal,
polyphenylene oxide, polybutylene terephthalate,
ethylene-propylene-diene terpolymer (EPDM), sulfonated
ethylene-propylene-diene terpolymer, styrene butadiene rubber,
fluoride rubber, or various copolymers, but the binder is not
limited thereto and may be any suitable binder used in the art. An
amount of the binder may be about 1 part by weight to about 50
parts by weight based on 100 parts by weight of the negative active
material. In one embodiment, the amount of the binder may be about
1 part by weight to about 30 parts by weight, 1 part by weight to
about 20 parts by weight, or about 1 part by weight to about 15
parts by weight based on 100 parts by weight of the negative active
material.
[0093] The negative electrode may optionally further include a
conductive agent to provide a conductive pathway to the negative
active material, to thereby further improve electrical
conductivity. The conductive agent may be acetylene black, Ketjen
black, natural graphite, artificial graphite, carbon black,
acetylene black, carbon fiber, or the like; a metal powder or metal
fiber of copper, nickel, aluminum, or silver; or a mixture of one
or more (polymeric) conductive materials such as polyphenylene
derivative. However, the conductive agent is not limited thereto,
and any suitable conductive agent used in the art may be used.
Also, the crystalline carbonaceous material may be further added as
the conductive agent. An amount of the conductive agent may be
appropriately controlled. For example, the conductive agent may be
added in such an amount that a weight ratio of the negative active
material to the conductive agent is in a range of about 99:1 to
about 90:10.
[0094] The solvent may be N-methylpyrrolidone (NMP), acetone,
water, or the like, but the solvent is not limited thereto and may
be any suitable solvent used in the art.
[0095] Amounts of the negative active material, the conductive
agent, the binder, and the solvent are amounts suitable for a
lithium battery. One or more of the conductive agent, the binder,
and the solvent may be omitted depending on the use and composition
of a lithium battery.
[0096] Also, the current collector may be formed in a thickness of
about 3 .mu.m to about 500 .mu.m. The current collector is not
particularly limited as long as the current collector does not
cause a chemical change in a battery and has conductivity. Examples
of a suitable material that forms the current collector are copper,
stainless steel, aluminum, nickel, titanium, calcined carbon,
copper and stainless steel that are surface-treated with carbon,
nickel, titanium, silver, or the like, an alloy of aluminum and
cadmium, etc. Also, an uneven micro structure may be formed on the
surface of the current collector to enhance a binding strength to
the negative active material. Also, the current collector may be
used in various forms including a film, a sheet, a foil, a net, a
porous structure, a foaming structure, a non-woven structure,
etc.
[0097] A lithium battery according to an embodiment includes a
negative electrode including the negative active material. The
lithium battery may be manufactured as follows:
[0098] First, a negative electrode is prepared according to a
method of preparing the negative electrode.
[0099] Then, a positive active material composition, in which a
positive active material, a conductive agent, a binder, and a
solvent are mixed, is prepared. The positive active material
composition is directly coated and dried on a metal current
collector to prepare a positive electrode plate. Alternatively, the
positive active material composition may be cast on a separate
support and then a film peeled off from the support may be
laminated on a metal current collector to manufacture a positive
electrode plate.
[0100] The positive active material may necessarily include at
least one selected from the group consisting of lithium cobalt
oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt
aluminum oxide, lithium iron phosphate, and lithium manganese
oxide, but the positive active material is not necessarily limited
thereto and may be any suitable positive active material used in
the art.
[0101] For example, at least one compound represented by any one
formula of Li.sub.aA.sub.1-bL.sub.bD.sub.2 (wherein,
0.90.ltoreq.a.ltoreq.1.8 and 0.ltoreq.b.ltoreq.0.5);
Li.sub.aE.sub.1-bL.sub.bO.sub.2-cD.sub.c (wherein,
0.90.ltoreq.a.ltoreq.1.8, 0.ltoreq.b.ltoreq.0.5, and
0.ltoreq.c.ltoreq.0.05); LiE.sub.2-bL.sub.bO.sub.4-cD.sub.c
(wherein, 0.ltoreq.b.ltoreq.0.5 and 0.ltoreq.c.ltoreq.0.05);
Li.sub.aNi.sub.1-b-cCo.sub.bL.sub.cD.sub.a (wherein,
0.90.ltoreq.a.ltoreq.1.8, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<a.ltoreq.2);
Li.sub.aNi.sub.1-b-cCo.sub.bL.sub.cO.sub.2-aM.sub.a (wherein,
0.90.ltoreq.a.ltoreq.1.8, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<a<2);
Li.sub.aNi.sub.1-b-cCo.sub.bL.sub.cO.sub.2-aM.sub.2 (wherein,
0.90.ltoreq.a.ltoreq.1.8, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<a<2);
Li.sub.aNi.sub.1-b-cMn.sub.bL.sub.cD.sub.a (wherein,
0.90.ltoreq.a.ltoreq.1.8, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<a.ltoreq.2);
Li.sub.aNi.sub.1-b-cMn.sub.bL.sub.cO.sub.2-aM.sub.a (wherein,
0.90.ltoreq.a.ltoreq.1.8, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<a<2);
Li.sub.aNi.sub.1-b-cMn.sub.bL.sub.cO.sub.2-aM.sub.2 (wherein,
0.90.ltoreq.a.ltoreq.1.8, 0.ltoreq.b.ltoreq.0.5,
0.ltoreq.c.ltoreq.0.05, and 0<a<2);
Li.sub.aNi.sub.bE.sub.cG.sub.dO.sub.2 (wherein,
0.90.ltoreq.a.ltoreq.1.8, 0.ltoreq.b.ltoreq.0.9,
0.ltoreq.c.ltoreq.0.5, and 0.001.ltoreq.d.ltoreq.0.1);
Li.sub.aNi.sub.bCo.sub.cMn.sub.dGeO.sub.2 (wherein,
0.90.ltoreq.a.ltoreq.1.8, 0.ltoreq.b.ltoreq.0.9,
0.ltoreq.c.ltoreq.0.5, 0.ltoreq.d.ltoreq.0.5, and
0.001.ltoreq.e.ltoreq.0.1); Li.sub.aNiG.sub.bO.sub.2 (wherein,
0.90.ltoreq.a.ltoreq.1.8 and 0.001.ltoreq.b.ltoreq.0.1);
Li.sub.aCoG.sub.bO.sub.2 (wherein, 0.90.ltoreq.a.ltoreq.1.8 and
0.001.ltoreq.b.ltoreq.0.1); Li.sub.aMnG.sub.bO.sub.2 (wherein,
0.90.ltoreq.a.ltoreq.1.8 and 0.001.ltoreq.b.ltoreq.0.1);
Li.sub.aMn.sub.2G.sub.bO.sub.4 (wherein, 0.90.ltoreq.a.ltoreq.1.8
and 0.001.ltoreq.b.ltoreq.0.1); QO.sub.2; QS.sub.2; LiQS.sub.2;
V.sub.2O.sub.5; LiV.sub.2O.sub.5; LiRO.sub.2; LiNiVO.sub.4;
Li.sub.(3-f)J.sub.2(PO.sub.4).sub.3(0.ltoreq.f.ltoreq.2);
Li.sub.(3-f)Fe.sub.2(PO.sub.4).sub.3(0.ltoreq.f.ltoreq.2); and
LiFePO.sub.4 may be used.
[0102] In the formulae above, A is Ni, Co, Mn, or a combination
thereof; L is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth metal
element, or a combination thereof; D is O, F, S, P, or a
combination thereof; E is Co, Mn, or a combination thereof; M is F,
S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, lanthanum
(La), cerium (Ce), Sr, V, or a combination thereof; Q is Ti, Mo,
Mn, or a combination thereof; R is Cr, V, Fe, Sc, Y, or a
combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a
combination thereof.
[0103] The compound may have a coating layer thereon, or the
compound and a compound having a coating layer thereon may be mixed
together. The coating layer may include a coating element compound
of an oxide of a coating element, a hydroxide of the coating
element, an oxyhydroxide of the coating element, an oxycarbonate of
the coating element, or a hydroxycarbonate of the coating element.
The compound forming the coating layer may be amorphous or
crystalline. The coating element included in the coating layer may
be Mg, Al, Co, potassium (K), sodium (Na), calcium (Ca), Si, Ti, V,
Sn, Ge, gallium (Ga), B, arsenic (As), Zr, or a combination
thereof. A method of forming the coating layer may be any suitable
method (for example, spray coating or immersion) that does not
negatively affect properties of the positive electrode by using the
element in the compound, and the method is known to one of ordinary
skill in the art and thus, the description thereof will not be
repeated herein.
[0104] For example, LiNiO.sub.2, LiCoO.sub.2, LiMn.sub.xO.sub.2x
(x=1, 2), LiNi.sub.1-xMn.sub.xO.sub.2 (0<x<1),
LiNi.sub.1-x-yCo.sub.xMn.sub.yO.sub.2 (0.ltoreq.x.ltoreq.0.5,
0.ltoreq.y.ltoreq.0.5), LiFeO.sub.2, V.sub.2O.sub.5, TiS, or MoS
may be used.
[0105] The conductive agent, the binder, and the solvent in the
positive active material composition may be the same as those in
the negative active material composition. Also, a plasticizer may
be further added to the positive active material composition and/or
negative active material composition to form pores inside an
electrode plate.
[0106] Amounts of the positive active material, the conductive
agent, the binder, and the solvent are amounts generally used in a
lithium battery. One or more of the conductive agent, the binder,
and the solvent may be omitted depending on use and composition of
a lithium battery.
[0107] Then, a separator to be inserted between the positive
electrode and the negative electrode is prepared. The separator may
be any suitable separator used for a lithium battery. The separator
may have a low resistance to migration of ions of an electrolyte
and a suitable (e.g., an excellent) electrolytic solution-retaining
capability. For example, the separator may be selected from the
group consisting of glass fiber, polyester, Teflon, polyethylene,
polypropylene, polytetrafluoroethylene (PTFE), and a combination
thereof, each of which may be nonwoven or woven. For example, a
separator that may be rolled, such as polyethylene or
polypropylene, may be used in a lithium ion battery, and a
separator having a suitable (e.g., an excellent) solution-retaining
capability may be used in a lithium ion polymer battery. For
example, the separator may be prepared by the method described
below.
[0108] A polymer resin, a filler, and a solvent are mixed to
prepare a separator composition. The separator composition may be
directly coated and then dried on an electrode to prepare a
separator. Alternatively, the separator composition may be cast and
then dried on a support, and a separator film peeled off from the
support may be laminated on the electrode to prepare a
separator.
[0109] The polymer resin used for preparing the separator is not
particularly limited and any suitable material used (utilized) as a
separator for an electrode plate may be used. For example,
vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene
fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a
combination thereof may be used.
[0110] Then, an electrolyte is prepared.
[0111] The electrolyte includes a non-aqueous electrolyte and a
lithium salt. The non-aqueous electrolyte may be a non-aqueous
electrolyte, an organic solid electrolyte, or an inorganic solid
electrolyte.
[0112] The non-aqueous electrolyte may be, for example, an aprotic
organic solvent such as N-methyl-2-pyrrolidinone, propylene
carbonate, ethylene carbonate, butylene carbonate, dimethyl
carbonate, diethyl carbonate, gamma-butyrolactone,
1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran,
dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-dioxolane, formamide,
N, N-dimethyl formamide, acetonitrile, nitromethane, methyl
formate, methyl acetate, phosphoric acid triester,
trimethoxymethane, a dioxolane derivative, sulfolane, methyl
sulfolane, 1,3-dimethyl-2-imidazolinone, a propylene carbonate
derivative, a tetrahydrofuran derivative, ether, methyl propionate,
or ethyl propionate.
[0113] The organic solid electrolyte may be, for example, a
polyethylene derivative, a polyethylene oxide derivative, a
polypropylene oxide derivative, a phosphoric acid ester polymer,
polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, or a
polymer containing an ionic dissociation group.
[0114] The inorganic solid electrolyte may be, for example, Li
nitride, halogenide, sulfide, or silicate, such as Li.sub.3N, LiI,
Li.sub.5NI.sub.2, Li.sub.3N--LiI--LiOH, LiSiO.sub.4,
LiSiO.sub.4--LiI--LiOH, Li.sub.2SiS.sub.3, Li.sub.4SiO.sub.4,
Li.sub.4SiO.sub.4--LiI--LiON, or
Li.sub.3PO.sub.4--Li.sub.2S--SiS.sub.2.
[0115] The lithium salt may be any suitable salt used in a lithium
battery. As a material that may be thoroughly dissolved in the
non-aqueous electrolyte, for example, at least one of LiCl, LiBr,
LiI, LiCIO.sub.4, LiBF.sub.4, LiB.sub.10Cl.sub.10, LiPF.sub.6,
LiCF.sub.3SO.sub.3, LiCF.sub.3CO.sub.2, LiAsF.sub.6, LiSbF.sub.6,
LiAlCl.sub.4, CH.sub.3SO.sub.3Li, CF.sub.3SO.sub.3Li,
(CF.sub.3SO.sub.2).sub.2NLi, lithium chloroborate, lower aliphatic
carbonic acid lithium, 4-phenyl boric acid lithium, lithium imide,
etc., may be used.
[0116] Lithium batteries may be categorized into lithium ion
batteries, lithium ion polymer batteries, or lithium polymer
batteries, according to a separator used and an electrolyte used.
Lithium batteries may also be categorized into cylindrical lithium
batteries, rectangular lithium batteries, coin-shaped lithium
batteries, or pouch-shaped lithium batteries, according to the
shape thereof. Lithium batteries may also be categorized as bulk
lithium batteries or thin layer lithium batteries, according to the
size thereof. The lithium batteries may also be primary batteries
or secondary batteries.
[0117] A method of manufacturing a lithium battery is known to one
of ordinary skill in the art, and thus, will not be described in
more detail herein.
[0118] FIG. 3 is a schematic view showing a structure of a lithium
battery 30 according to an embodiment.
[0119] Referring to FIG. 3, the lithium battery 30 includes a
positive electrode 23, a negative electrode 22, and a separator 24
interposed between the positive and negative electrodes 22 and 23.
The positive electrode 23, the negative electrode 22, and the
separator 24 are wound or folded to be housed in a battery case 25.
Then, an electrolyte is injected into the battery case 25, followed
by sealing the battery case 25 with an encapsulation member 26,
thereby completing the manufacture of the lithium battery 30. The
battery case 25 may be a cylindrical, a rectangular, or a thin film
case. The lithium battery 30 may be a lithium ion battery.
[0120] A lithium battery according to an embodiment may be used in
an application such as an electric vehicle that requires high
capacity, high power output, and high-temperature driving, in
addition to existing mobile phones or portable computers. Also, the
lithium battery may be combined with an existing
internal-combustion engine, a fuel cell, a super capacitor, or the
like, for use in a hybrid vehicle or the like. For example, the
lithium battery has excellent high rate capability and lifespan
characteristics and thus, is suitable for an electric vehicle (EV).
For example, the lithium battery is suitable for a plug-in hybrid
electric vehicle (PHEV).
[0121] A method of preparing a negative active material according
to another embodiment includes:
[0122] mixing a crystalline carbonaceous substrate, a metal oxide
precursor, and a solvent to prepare a mixture solution;
[0123] drying the mixture solution to prepare a dried product;
and
[0124] heat treating the dried product.
[0125] The metal oxide precursor may be a metal salt including at
least one metal selected from the group consisting of Ti, Zr, Ni,
Co, Mn, Cr, Zn, Mo, Ta, B, Mg, Ca, Sr, Ba, V, Fe, Cu, and Al. The
metal salt may be a hydride, an oxyhydride, an alkoxide, a sulfate,
a nitrate, and/or a carbonate.
[0126] For example, metal alkoxide may be used as a metal oxide
derivative. The metal alkoxide may be an organic metal compound in
which an alkoxide group is coordinated to a metal ion and may be in
a sol form.
[0127] For example, the metal alkoxide may be represented by
Formula 2 below.
M(OR).sub.x Formula 2
[0128] wherein, 1.ltoreq.x.ltoreq.5 and M is selected from the
group consisting of Ti, Zr, Ni, Co, Mn, Cr, Zn, B, Mg, Ca, Sr, Ba,
V, Fe, Cu, Mo, Nb, Ta, and Al.
[0129] A weight ratio of the crystalline carbonaceous substrate to
the metal oxide precursor may be about 100:0.01 to about 100:20,
for example, about 100:0.01 to about 100:10, about 100:0.1 to about
100:5, or about 100:0.1 to about 100:1. When the amount of the
metal alkoxide is too small, an amount of the coating may be small
and thus, coating effects may be small, and when the amount of the
metal alkoxide is too great, the specific capacity of the battery
may decrease.
[0130] The solvent may be water, alcohol, or a combination thereof,
and the alcohol may be a C1-C4 lower alcohol, examples of which are
methanol, ethanol, isopropanol, or a combination thereof. However,
the solvent is not limited thereto, and any suitable solvent known
in the related art that may be used to achieve the objective of the
manufacturing method may be utilized.
[0131] In the manufacturing method described above, the crystalline
carbonaceous substrate, the metal oxide precursor, and the solvent
may be mixed to prepare a mixture solution, the mixture solution
may be dried to obtain a dried product, and the dried product may
be heat treated to obtain a negative active material in which metal
oxide nanoparticles are formed on the surface of the crystalline
carbonaceous substrate.
[0132] According to an embodiment, the heat treatment may be
performed in a nitrogen or atmospheric (air) environment at a
temperature of 700.degree. C. or greater. At a heat treatment
temperature of 700.degree. C. or greater, a rutile phase may be
formed, and at 700.degree. C. or less, only an anatase phase may be
obtained. For example, when the heat treatment temperature is
700.degree. C. or greater but less than 800.degree. C., a mixture
of both the anatase phase and the rutile phase may be obtained, and
when the heat treatment temperature is 800.degree. C. or greater,
metal oxide nanoparticles, in which only the rutile phase is
present, may be formed. According to an embodiment, the heat
treatment may be performed at a temperature of about 700.degree. C.
to about 900.degree. C. for about 30 minutes to about 10 hours.
[0133] The manufacturing method may further include grinding a heat
treatment product obtained from the heat treatment.
[0134] Also, the negative active material may be prepared by a dry
method including mechanically mixing the metal oxide particles with
the crystalline carbonaceous substrate to form a coating layer
including the metal oxide nanoparticles on the crystalline
carbonaceous substrate, in addition to the wet method described
above. The mixing method may be a mechanofusion method or the like.
Also, the dry method may further include forming the metal oxide
nanoparticles on the crystalline carbonaceous substrate and then
heat treating the same.
[0135] Hereinafter, example embodiments will be described in more
detail with reference to examples. However, the examples are for
illustrative purposes only and do not limit the scope.
Preparing a Negative Active Material
Manufacturing Example 1
0.5 wt % Rutile Coating Phase
[0136] As a carbonaceous substrate, 25 g of natural graphite powder
(a product of Hitachi Chemical) having an average diameter of about
10 .mu.m, and 0.44 g of titanium isopropoxide
((Ti(OCH(CH.sub.3).sub.2).sub.4, a product of Aldrich, and product
No: 205273) were added to 200 ml of isopropyl alcohol and then
mixed to prepare a mixture solution. In a heatable stirrer, the
mixture solution was stirred at a temperature of 100.degree. C. at
300 rpm while removing a solvent to obtain a dried powder. The
dried powder was calcined in nitrogen (N.sub.2) atmosphere at a
temperature of 800.degree. C. for 1 hour to obtain a calcined
product. The calcined product was pulverized to prepare a negative
active material coated with TiO.sub.2 nanoparticles having a rutile
phase in an amount of 0.5 wt % on a surface of the natural
graphite.
Manufacturing Example 2
0.5 wt % Rutile+Anatase Coating Phases
[0137] A negative active material was prepared in the same manner
as in Manufacturing Example 1, except that a calcination
temperature was changed to 700.degree. C.
Comparative Manufacturing Example 1
0.5 wt % Anatase Coating Phase
[0138] A negative active material was prepared in the same manner
as in Manufacturing Example 1, except that a calcination
temperature was changed to 600.degree. C.
Comparative Manufacturing Example 2
Without Coating Treatment
[0139] Natural graphite (a product of Hitachi Chemical) having an
average diameter of about 10 .mu.m without any coating treatment on
the surface thereof was used as a negative active material.
Evaluation Example 1
Analysis of Coating State
[0140] To analyze a coating state of the negative active material
prepared in Manufacturing Example 1, Field Emission Scanning
Electron Microscope (FE-SEM) images of a natural graphite substrate
before and after calcination are shown in FIGS. 4A and 4B.
[0141] As shown in FIGS. 4A and 4B, it may be concluded that
TiO.sub.2 nanoparticles were coated as an island shape (as a
discontinuous layer) on the surface of the natural graphite after
the calcination. The graphite negative active material coated with
the TiO.sub.2 nanoparticles as an island shape may have better
lithium ion mobility than the graphite negative active material
coated with the TiO.sub.2 nanoparticles in a complete (or
continuous) layer form.
Evaluation Example 2
XRD Analysis
[0142] FIG. 5 shows XRD analysis results of the negative active
materials prepared in Manufacturing Example 1 and Comparative
Manufacturing Example 1 obtained by using CuK.alpha. rays. In FIG.
5, R stands for a rutile phase and A stands for an anatase phase of
TiO.sub.2.
[0143] As shown in FIG. 5, graphite coated with titanium
isopropoxide that is heat treated at a temperature of 800.degree.
C. shows TiO.sub.2 only in a rutile phase and graphite coated with
titanium isopropoxide that is heat treated at a temperature of
700.degree. C. has TiO.sub.2 in a mixture phase of rutile and
anatase, and graphite heat treated at a temperature of 600.degree.
C. has TiO.sub.2 only in an anatase phase.
[0144] In addition, to identify the change in a crystalline phase
of TiO.sub.2 according to a heat treatment temperature, a titanium
isopropoxide solution removed of graphite was heat treated at a
temperature of 600.degree. C., 700.degree. C., 800.degree. C., and
900.degree. C., and the TiO.sub.2 nanoparticles obtained therefrom
were subjected to an XRD analysis and the results obtained
therefrom are shown in FIG. 6.
[0145] As shown in FIG. 6, a product obtained from heat treatment
at a temperature of 800.degree. C. (or higher) only showed a rutile
phase and a product obtained from heat treatment at a temperature
of 700.degree. C. showed a mixed phase of rutile and anatase, and a
product obtained from heat treatment at a temperature of
600.degree. C. only showed an anatase phase. These results match
the results obtained from FIG. 5.
Manufacturing Coin Half-Cells
[0146] Coin half-cells were manufactured as follows to analyze
changes in high temperature storage characteristics and thermal
stability according to a TiO.sub.2 coating:
Example 1
[0147] The negative active material prepared in Manufacturing
Example 1 and poly amide imide (PAI) as a binder were mixed at a
weight ratio of 90:10 to prepare a negative active material
slurry.
[0148] The negative active material slurry was coated on a copper
foil current collector having a thickness of 10 .mu.m at 9
mg/cm.sup.2. The coated electrode plate was dried at a temperature
of 120.degree. C. for 15 minutes and then pressed to manufacture a
negative electrode.
[0149] As a counter electrode, a Li metal was used; as a separator,
a polyethylene separator (STAR 20, a product of Asahi) was used;
and as an electrolyte, 1.15 M LiPF.sub.6 dissolved in a mixture
solvent of ethylene carbonate (EC):ethyl methyl carbonate
(EMC):diethyl carbonate (DEC) (at a volume ratio of 3:3:4) was used
(utilized) to manufacture a coin half-cell.
Example 2
[0150] A coin half-cell was manufactured in the same manner as in
Manufacturing Example 1, except that the negative active material
of Manufacturing Example 2 was used instead of the negative active
material of Manufacturing Example 1.
Comparative Example 1
[0151] A coin half-cell was manufactured in the same manner as in
Example 1, except that the negative active material of Comparative
Manufacturing Example 2 was used instead of the negative active
material of Manufacturing Example 1.
Evaluation Example 3
Evaluation of High Temperature Storage Characteristics
[0152] The coin half-cells manufactured in Example 2 and
Comparative Example 1 were fully charged at 0.01 V (0.01 C cutoff)
to store the same at a temperature of 90.degree. C. for three days.
A Solatron apparatus (model name: 1260 FRA) was used to measure the
AC-impedance before and after storage at an alternating current of
0.5 mA in a range of about 1000 Hz to about 0.1 Hz, and the results
obtained therefrom are shown in FIG. 7.
[0153] As shown in FIG. 7, graphite coated with TiO.sub.2 showed
smaller increase in impedance at high temperature storage
characteristics than graphite that is not coated with TiO.sub.2.
This shows that graphite coated with TiO.sub.2 has improved high
temperature storage characteristics than graphite not coated with
TiO.sub.2.
Evaluation Example 4
Evaluation of Thermal Stability
[0154] The coin half-cells manufactured in Example 1 and
Comparative Example 1 were charged with a constant current at 0.1 C
CC/CV until a voltage reached 4.3 V (vs. Li). After reaching the
voltage of 4.3 V, the coin half-cells were charged at 4.3 V until a
value of constant current was reduced to 1/10.sup.th of the
original value. After the charging, the coin half-cells were
disassembled in a dry room, such that interference did not occur
between two electrodes, and then a sampling on the mixture of a
negative electrode was taken and the thermal stability thereof was
evaluated. The evaluation of thermal stability was performed by
differential scanning calorimetry (DSC) analysis, wherein
temperatures of the mixture of a negative electrode were increased
at intervals of 10.degree. C. in a range of 30.degree. C. to
400.degree. C. to measure an amount of heat generated by the
negative active material within the mixture of a negative electrode
due to a reaction with an electrolyte according to temperature,
which was converted into a mass unit.
[0155] FIG. 8 shows DSC results of the coin half-cells manufactured
in Example 1 and Comparative Example 1. Here, region A is a heat
generation region of a film decomposition process and region B is a
temperature (exothermal) region in which a charged negative active
material is decomposed.
[0156] As shown in FIG. 8, a graphite negative active material
coated with TiO.sub.2 showed a smaller heat generation peak near
300.degree. C. compared to the graphite negative active material
that is not coated with TiO.sub.2. This shows that lithiated
TiO.sub.2 has a more stable structure than lithiated graphite and
thus, shows a smaller heat generation peak in region B. The results
described above suggest that the thermal stability of the negative
active material is improved due to the TiO.sub.2 coating.
Manufacturing a Coin Full Cell
[0157] To evaluate high temperature lifespan characteristics, a
coin full cell was manufactured as follows:
Example 3
[0158] The negative active material manufactured in Manufacturing
Example 1 was mixed with a binder (in which styrene butadiene
rubber (SBR) was mixed with carboxymethyl cellulose (CMC) at a
ratio of 1:1) at a ratio of 98:2 to prepare a negative active
material slurry.
[0159] The negative active material slurry was coated on a copper
foil current collector having a thickness of 10 .mu.m at 9
mg/cm.sup.2. After the coating, the coated electrode plate was
dried at a temperature of 120.degree. C. for 15 minutes, and then
pressed to manufacture a negative electrode.
[0160] As a positive electrode, LiCoO.sub.2 (LCO), which was a
positive active material, carbon black, which was a conductor, and
polyvinylidene fluoride (PVdF), which was a binder, were mixed at a
weight ratio of 97.5:1:1.5 to prepare a positive active material
slurry.
[0161] The positive active material slurry was coated on an
aluminum foil current collector having a thickness of 12 .mu.m at
18 mg/cm.sup.2, and the coated electrode plate was dried at a
temperature of 120.degree. C. for 15 minutes, and then pressed to
manufacture a positive electrode.
[0162] The above prepared positive electrode and the above prepared
negative electrode, a polyethylene separator as a separator (STAR
20, a product of Asahi), and 1.15M LiPF.sub.6 dissolved in a
mixture solvent of EC:EMC:DEC (volume ratio of 3:3:4) as an
electrolyte were used to manufacture a coin cell.
Example 4
[0163] A coin full cell was manufactured in the same manner as in
Example 1, except that the negative active material manufactured in
Manufacturing Example 2 was used instead of the negative active
material manufactured in Manufacturing Example 1.
Comparative Example 2
[0164] A coin full cell was manufactured in the same manner as in
Example 1, except that the negative active material manufactured in
Comparative Manufacturing Example 1 was used instead of the
negative active material manufactured in Manufacturing Example
1.
Comparative Example 3
[0165] A coin full cell was manufactured in the same manner as in
Example 1, except that the negative active material manufactured in
Comparative Manufacturing Example 2 was used instead of the
negative active material manufactured in Manufacturing Example
1.
Evaluation Example 5
Evaluation of High Temperature Lifespan Characteristics
[0166] To evaluate high temperature lifespan characteristics of the
coin full cells manufactured in Examples 3 and 4 and Comparative
Examples 2 and 3, each coin full cell was charged by using constant
current at a 0.2 C rate until a voltage reached 0.01 V (vs. Li) at
a temperature of 45.degree. C., maintained at 0.01 V, and then
charged at constant current until a current of 0.01 C was reached.
Thereafter, the coin full cell was discharged at constant current
of 0.2 C until a voltage of 1.5 V (vs. Li) was reached.
[0167] Thereafter, the coin full cell was charged at constant
current at a current at a 0.5 C rate until a voltage of 0.01 V (vs.
Li) was reached, maintained at 0.01 V, and then charged at constant
current until a current of 0.01 C was reached. Thereafter, the coin
full cell was discharged at a constant current of 0.5 C until a
voltage of 1.5 V (vs. Li) was reached (formation process).
[0168] The coin full cells after the formation process were charged
at constant current at a 1.0 C rate at a temperature of 60.degree.
C. until a voltage of 0.01 V (vs. Li) was reached, maintained at
0.01 V, and then charged at a constant current until a current of
0.01 C was reached. Thereafter, a cycle of discharging at a
constant current of 1.0 C until a voltage of 1.5 V (vs. Li) was
reached was repeated 50 times.
[0169] Capacity retention ratios (CRR) of the coin full cells
manufactured in Examples 3 and 4, and Comparative Examples 2 and 3
at a high temperature are shown in FIG. 9. The CRR is defined by
Equation 1 below.
Capacity retention ratio [%]=[discharge capacity in each
cycle/discharge capacity in the first cycle].times.100 Equation
1
[0170] As shown in FIG. 9, high temperature lifespan
characteristics of the coin full cells including TiO.sub.2
nanoparticles having a rutile structure (Example 3) and the coin
full cell including TiO.sub.2 nanoparticles in which a rutile
structure and an anatase structure were mixed (Example 4) showed
high temperature lifespan characteristics compared to the coin full
cell in which graphite was not coated with TiO.sub.2 nanoparticles
(Comparative Example 3). However, the coin full cell including the
TiO.sub.2 nanoparticles having an anatase structure (Comparative
Example 2) showed deteriorated high temperature characteristics
compared to the coin full cell in which graphite was not coated
with TiO.sub.2 nanoparticles (Comparative Example 3).
[0171] As described above, according to the one or more of the
above embodiments of the present invention, negative active
materials may be used to improve high temperature stability and
lifespan characteristics of a lithium battery.
[0172] It should be understood that the example embodiments
described therein should be considered in a descriptive sense only
and not for purposes of limitation. Descriptions of features or
aspects within each embodiment should typically be considered as
available for other similar features or aspects in other
embodiments.
* * * * *